The present invention relates to a semiconductor laser used as a light source for a laser printer, a bar cord reader, or the like and, more particularly, to a method of manufacturing a visible-light semiconductor laser having an oscillation wavelength of 680 nm or less.
A conventional method of manufacturing a semiconductor laser will be described below. The structure of a semiconductor laser is shown in FIG. 4. According to the conventional method of manufacturing a semiconductor laser, as the first crystal growth, a GA.sub.0.5 In.sub.0.5 P active layer 4 serving as a luminescent region is formed on a GaAs substrate 1 at a growth temperature of 700 to 730.degree. C. by metal organic-vapor phase epitaxy (to be referred to as MO-VPE hereinafter) to be interposed between (Al.sub.0.7 Ga.sub.0.3).sub.0.5 In.sub.0.5 P cladding layers 3 and 5 each of which has a forbidden band larger than that of the GA.sub.0.5 In.sub.0.5 P active layer 4, thereby forming a double-hetero structure.
An oxide film serving as an etching mask for a ridge stripe and a mask for selective growth is formed, and an oxide film stripe is formed in a [0-11] direction by a photoresist method. The resultant structure is etched up to the middle of the p-type cladding layer 5.
Subsequently, the second crystal growth is performed, i.e., selective growth is performed using an oxide film as a mask to form a current blocking layer 7. After the oxide film is removed, a p-type GaAs contact layer 8 is grown on the entire surface of the resultant structure, and electrodes 9 and 10 are arranged, thereby obtaining a conventional semiconductor laser.
A threshold current value of the characteristics of the conventional semiconductor laser considerably depends on the Zn carrier concentration in the p-type cladding layer 5. For example, it is reported that the threshold current value is 38 mA at a carrier concentration of 3.5.times.10.sup.17 cm.sup.-3. At this time, the cavity length is 300 .mu.m, and the maximum continuous wave oscillation temperature is 100.degree. C., but the reliability of the conventional laser is not reported. The conventional laser is described in the Extended Abstracts of the 36th Spring Meeting Japanese Society Applied Physics, 1989 p. 886 1p-ZC-4.
In a GA.sub.0.5 In.sub.0.5 P layer used in an AlGaInP semiconductor laser according to the present invention, as reported in Jpn. J. Appl Phys Vol. 27, No. 11, November, 1988, pp. 2089-2106, a band-gap Eg is changed in accordance with a crystal growth temperature Tg in MO-VPE. When the growth temperature is increased, a semiconductor laser having a short emission wavelength. However, when the growth temperature is increased, Zn doping in the p-type cladding layer 5 is generally difficult. Furthermore, Zn doped in an (Al.sub.y Ga.sub.1-y).sub.0.5 In.sub.0.5 P layer is easily diffused. As the growth temperature is increased, the diffusion further progresses. More specifically, when the Zn is doped in an active layer, the reliability of the semiconductor laser is degraded. For this reason, a semiconductor laser having practical characteristics cannot be easily obtained.